Methods of preparing metal-coated articles are known. For instance, Orban in U.S. Pat. No. 4,645,573 discloses continuous processes for coating polyester filaments with copper and silver involving, as illustrated in FIG. 1A, a plurality of steps, including cleaning, wetting and etching of the filament prior to contacting with commercial palladium chloride/stannous chloride catalytic activator, followed by an acid bath, electroless copper plating, copper cyanide plating and silver cyanide plating. See also U.S. Pat. No. 4,645,574 where Orban discloses continuous processes for coating polyamide filaments which as illustrated in FIG. 1B requires the use of a preactivator. Matijevic et al. in a paper entitled: "The Characterization of the Stannous Chloride/Palladium Chloride Catalysts for Electroless Plating", Plating And Surface Finishing, Oct. 1975, p.958, indicate that colloidal palladium is necessary for catalytic activity and that solutions of palladium complexes do not act as catalysts.
In view of methods disclosed in the prior art, e.g. as illustrated by Orban and Matijevic et al., one object of this invention is to provide simpler methods for the metal coating of articles, e.g. filaments, with fewer required process steps and the common intermediate washing steps that generate waste disposal problems. It is a further object of this invention to provide such articles with an oxidation-resistant, electrolessly-deposited copper coating that requires the additional treatment of electrodeposition to provide oxidation resistance.
Others have proposed the use of binders to promote the adhesion of high levels of catalytic activator. See for instance Sirinyan, et al., who disclose in U.S. Pat. No. 4,493,861 the use of palladium complexes of polybutadiene in coating solutions comprising as least about 5.2 weight percent palladium. See also Brandt, et al., who disclose in U.S. Pat. No. 3,930,109 the application of catalytic coatings comprising polymeric binder with at least about 0.4 weight percent palladium chloride. Because of the high cost of catalytic compounds, e.g. palladium compounds, it would be desirable to be able to utilize solutions comprising lower levels of catalytic metal.